WASHINGTON – Russia now has “complete operational control” of the Crimean Peninsula with 6,000-plus airborne and naval forces “with considerable material,” U.S. officials conceded late Sunday.

In a briefing to reporters, they said “there is no question that they are in an occupation position in Crimea, that they are flying in reinforcements, and they’re settling in … that is the situation that we confront.”

One senior official said the Ukraine government is showing considerable restraint by keeping Ukrainian soldiers in their bases. In some cases, they have “locked their weapons up.”

Another senior official said, however, “the longer this situation goes on, the more delicate it becomes.”

The official added: “We are concerned as we watch this situation that the Russians have badly miscalculated here. There is a very proud and fierce tradition in Ukraine of defending their sovereignty and territorial integrity.”

With Russian troops carrying out exercises on Ukraine’s eastern border, the concern is whether Russia plans to extend its control beyond Crimea.

Western containment strategy is to concentrate on isolating Russia diplomatically and economically, one official said.

U.S. Secretary of State John Kerry warned Russia Sunday that it is in danger of expulsion from the G8 group of industrialized nations and could be hit with trade sanctions and asset freezes unless it returns its military forces in Ukraine to their bases.

The G7 countries — Canada, United States, United Kingdom, France, Germany, Italy and Japan — stopped short, however, of outright withdrawal from the planned G8 summit in Russia. Instead, they announced their decision in an official statement late Sunday to “suspend their participation in activities associated with the preparation of the scheduled G8 Summit in Sochi in June until the environment comes back where the G8 is able to have meaningful discussion.”

The G7 countries said that Russia’s actions in Ukraine contravene the “principles and values on which the G7 and the G8 operate.”

In a series of appearances on U.S. Sunday morning news shows, Kerry, who will visit Ukraine on Tuesday as a sign of support for the government, said the suspension is retaliation for Russia’s “incredible act of aggression” against Ukraine.

Russian President Vladimir Putin “is going to lose on the international stage, Russia is going to lose, the Russian people are going to lose, and he’s going to lose all of the glow that came out of the Olympics, his $60 billion extravaganza,” Kerry said on NBC’s Meet the Press.

“There’s a unified view by all of the foreign ministers I talked with yesterday — all of the G8 and more — that they’re simply going to isolate Russia; that they’re not going to engage with Russia in a normal business-as-usual manner … The ruble is already going down and feeling the impact of this,” he said.

Other retaliatory actions could include denial of visas for Russians traveling to Europe and North America and the freezing of bank accounts.

Kerry’s strong condemnation of Russia raises the issue of how far the West is prepared to go to back Ukraine’s sovereignty. When Ukraine renounced its nuclear weapons in 1994, Russia, the United States and Britain signed the Budapest Memorandum on Security Assurances guaranteeing the country’s territorial integrity. It also guaranteed that none of the parties could use economic coercion against Ukraine. Although it was not a formal treaty, it is backed by the 1974 Helsinki Final Act Treaty that guaranteed Ukraine’s independence in the post-Soviet era. The Russian invasion of the autonomous Ukrainian region of Crimea violates that agreement, Western leaders claim.

Kerry called Russia’s military actions “19th century behaviour.” Then, in an indirect indictment of the U.S. invasion of Iraq in 2002 on trumped-up allegations of weapons of mass destruction, Kerry added, “You just don’t invade another country on phony pretexts in order to assert your interests.”

“It is really a stunning, wilful choice by President Putin to invade another country,” he told CBS’s Face the Nation.

He said Russia is in violation of the United Nations charter as well as several other international agreements.

Ukrainian Prime Minister Arseniy Yatsenyuk said Sunday morning his country is on the “brink of disaster” as it edges toward war with Russia.

Putin told U.S. President Barack Obama in a 90-minute phone call Saturday that “if the violence spreads further in the eastern regions of Ukraine and Crimea, Russia reserves the right to defend its interests and those of the Russian-speaking population that lives there.”

There is, however, no evidence that ethnic Russians in Ukraine have become targets of violence. Escalating protests by Ukrainians over the last four months have been aimed exclusively at the government of former president Viktor Yanukovych, who had suspended the Ukrainian constitution and who is widely viewed as a Russian puppet.

The protests forced Yanukovych and many of his cabinet members to flee to Russia, sparking the Russian military actions.

Kerry said Russia’s actions are not those of “someone who is strong; it’s the act of somebody who is acting out of weakness and out of a certain kind of desperation.”

Kerry said there are “all kinds of other options available to Russia (and) there still are.

“If you have legitimate concerns about your citizens, go to the United Nations, ask for observers, engage the other country’s government.”

Obama spent the weekend gathering support from Western leaders including Canada, the UK, Germany, France and Poland. According to the White House, the leaders affirmed the importance of unity in their support for the Ukraine and pledged to work together on a financial assistance package to help the country stabilize its economy.